This invention relates to a device and method for automatically controlling the feed from a distributive feeding device of the type used for feeding product to each weighing unit of an automatic combination weighing machine having circularly arranged weighing units.
A typical combination weighing machine of the circular array type includes, as shown in FIG. 1, a centrally disposed conical dispersion feeder 1, a plurality of linear conveyer troughs 2 (only two of which are shown) arranged radially therearound, a feed hopper 3 under each conveyer trough, a weigh hopper 4 under each feed hopper, a weight sensor 5 associated with each weigh hopper, a collection chute 6 common to all of the weigh hoppers, and a combination control device 7 for effecting arithmetic of the weight signals from the weight sensors 5 to discharge product from selected weigh hoppers 4, to the collection chute 6. The dispersion feeder 1 and the conveyer troughs 2 are independently supported on a common machine frame (not shown) through their own vibrating mechanisms 8 and 9, respectively. Generally, during the operation of this combination weighing machine in full-automatic fashion, the product to be weighed is lifted above the combination weighing machine by a carrying device 10, such as a bucket conveyer, and thrown through a horizontal feeder 11 into a funnel chute 12 disposed directly above the dispersion feeder 1. The product is dispersed radially over the dispersion feeder 1 by its vibration, and is fed onto each of the surrounding conveyer troughs 2 as a continuous layer of thickness h as shown. The product on these conveyer troughs 2 moves by the aid of independent vibration of each conveyer trough falls into its respective underlying feed hopper 3. Accordingly, it can be understood that the amount of product fed to each feed hopper 3 is generally a function of the vibration time of the corresponding conveyer trough 2 and the thickness h of the product layer on this trough. As is well known to those skilled in this field, it is important to control the weight of the product fed to the respective weigh hoppers 4 or to the corresponding feed hoppers 3, so these weights are as uniform as possible in order to improve the accuracy of the weight of product weighed out every time with respect to a predetermined target weight. However, even if the vibration time of each conveyer trough 2 is kept constant, it is very difficult to provide a uniform amount of feed because of variations in the thickness and apparent density of the product layer due to variations in the state of product caused by aggregation and entanglement, and there has been no way for adjusting the amount of feed other than time-consuming manual work of a skilled operator.
Japanese patent opening gazette No. 60-196626, discloses an attempt at a solution to the above-mentioned problem. According to this system, the horizontal displacement of the center of gravity of the product in the weigh hoppers is arithmetically determined by analyzing the weight signals from the respective weight sensors. The funnel chute 12 is then moved in the direction opposite from the direction of displacement of the center of gravity from the central axis of the above-mentioned dispersion feeder 1 to compensate for the deviation in the amount of feed in the respective hoppers. Although this system has exhibited a substantial effect in obtaining uniformity of the weight signals from the weighing units, it does not compensate for the accuracy of the combined weight of product whose weights were used as the bases of compensation, since this product is already in the weigh hoppers. In other words, this system has a fundamental shortcoming in that it does not completely eliminate inaccuracy and non-uniformity of the weight of the product to the weigh hoppers.
Accordingly, an object of this invention is to provide an improved control device and method which controls the weight of the product delivered to each weigh hopper.